Talk:Event Missions/@comment-30613790-20170407191731/@comment-28059753-20170408192341
I'll give it a shot, but keep in mind this is just an estimate and that I'm glossing over many details that may be important, and also making assumptions that may not be completely accurate for the sake of calculation. For collection, I'll model as a 90/12 mission with 4x item (5) and 2x item (3) both at 95% drop rate. AW Thief will raise drop rates to 100%. This is will result in collecting (1.00/.95) times as many items over the course of farming. (Lower drops rates mean the thief is actually more effective assuming the conventional wisdom the drop rate bonuses add like this, so this is conservative. However, note that some missions like our latest item collection seem to have 100% drop rates in which case a thief doesn't help at all. 95% seems like a decent guess for newer collections in DMM, though, e.g. this one.) Also, conservatively take 1200 items as the objective which is max CR in newer DMM collections. The amount of farming saved is 1200 - 1200/(1.00/.95) = 60 items. The base assumption is that the marginal cost of collection items is SC, but we can check that. The (thief-less) expected yield of our 90/12 mission is .95*4*5+.95*3*2 = 24.7 items. The mission can be run 28 times over two weeks on stamina regen or 37 times on charisma regen (plus maybe one or two fromo banking). 37*24.7 = 913.9 which is short of the 1200 target, so at the margin, SC is being spent on both stamina and charisma as expected. Assuming level 200, the average SC cost of the mission is (90/427 + 12/18) ~ 0.877. This makes the average cost in SC of each item at the margin ~ 0.877 / 24.7 ~ 0.0355 SC per item. So, if Leda saves farming 60 items, then the SC saved is ~ 60 * 0.0355 ~ 2.13 SC per farm event. (With more generous assumptions of 90% drop rate and 1400 target, it comes out to ~ 2.76 SC.) Now, what is the cost of getting Leda from the shrine? According to these rates, the best chance of getting her is if she's the only gold unit with summon chance up in premium summon. The chance of getting her from each summon then is 20% * 37% = 7.4% only. However, other summons are not worthless. I'll conservatively say that platinum and black units are "worth" the 5 SC cost, so count only other gold and below summons against the cost of farming Leda. She has 20%*(37%/87%) ~ 8.5% chance of appearing as gold or lower. Since it is a low chance, I'll just estimate the cost of farming her as the expected number of Leda per SC spent which is then ~ 0.085 / 5 ~ 0.017 Leda per SC or a cost of ~ 1 / 0.017 ~ 58.8 SC per Leda. (But keep in mind the variance in cost of getting a low-chance unit from the shrine is quite high.) Given these calculations, it would take over 27 item collection events for Leda to pay off. Not counting Liana's event, DMM has had I think only 9 item collections we haven't got yet. If the game continues forever, I guess she must pay off eventually, but on the other hand, there may be an easier way to get a thief before then... it is just unknown.